1. Field of the Invention
The present invention generally relates to Charged Particle Beam Projection Systems, and more particularly, to a laser-based method for fabricating high precision, thermally stable electromagnetic coil vanes used with Charged Particle Beam Projection Systems.
2. Background Description
Charged particle beam systems require a series of deflectors to control the path of electrons as they travel from their source (the electron gun) to their target (the electron sensitive resist being exposed). Ser. No. 09/324,899 discloses a toroidal style deflector composed of many individual coil vanes that provides high mechanical stability and accuracy. The fabrication of these coil vanes presents many challenges. They require uninsulated, low resistance (AWG 22-23) copper wiring, with a substantially rectangular cross-section. The copper wires must be precisely located upon and attached to both sides of a thin, insulating substrate with a low thermal coefficient of expansion. The wiring must be densely spaced (0.6 mm wide wires with 0.25 mm or less spaces) to provide sufficient performance. Moreover, the overall thickness of each coil vane should be a small as possible.
Ser. No. 09/325,162 describes one method to produce these coil vanes. Machined copper circuit patterns (approximately 0.5 mm thick) are mechanically aligned and bonded with a heat curable epoxy to both sides of a low expansion vane substrate. The process is somewhat complex, costly, and time consuming.
U.S. Pat. No. 6,461,680 describes a second method where the copper circuit pattern is formed via photolithography on a ceramic substrate and then plated and bonded. This process is less complex and less costly than that of Ser. No. 09/325,162, and can produce coils with improved pattern placement accuracy. The elimination of the epoxy bonding agent also reduces the overall vane thickness. The limitation of this process is that present technology limits the maximum attainable plated copper thickness to approximately 0.13 mm.
It is therefore an object of the invention to provide a simplified, cost effective coil vane fabrication technique using laser machining which has the advantages of providing an improved coil placement accuracy and wire density.
It is yet another object of the invention to provide a method for fabricating high precision, thermally stable electromagnetic coil vanes that do not require specialized tooling or a bonding composition to align and clamp the copper coils.
According to the invention, a laser-based method is provided to fabricate high current capacity, high accuracy, thermally stable deflection yokes used to generate off axis beam deflections. In the preferred embodiment, electromagnetic coil vanes are formed having by combining selected steps of the direct bond copper (DBC) method with laser machining to produce thin, extremely accurate, coil vanes with equivalent wire gauge (AWG 22-23), improved wire density, and a substantially rectangular wire cross-section.
In a preferred embodiment, a substrate, preferably made of thin alumina ceramic and preferably having a thickness of approximately 0.64 mm or less, has approximately 0.5 mm copper sheets bonded to each side. The copper sheets and ceramic are heated in a furnace to the melting point of copper oxide (which is lower than the melt point of copper). The copper oxide then melts and forms a permanent, xe2x80x9ceutecticxe2x80x9d bond between the copper and the ceramic.
The coil pattern is then xe2x80x9claser machinedxe2x80x9d through the copper sheets on each side of the substrate. Laser machining can form spaces between adjacent wires or turns of less than 0.1 mm, whereas the technique of Ser. No. 09/325,162 required the minimum space between adjacent wires to be at least 0.25 mm. The method of the present invention thus enables denser and, therefore, higher efficiency coils to be produced. The cross-section of the copper wire pattern is substantially rectangular.
Following the laser machining, a hole is drilled through the vane and an electrical connection made between the circuits on either side of the ceramic vane. Alternatively, the through connection could be formed in a pre-drilled hole in the ceramic during the direct bond copper process